In the field of oil and gas exploration and production, it is common for sand and other fine solid particles to be present in reservoir fluids. These particles are highly abrasive and cause damage to the well and its components, and therefore in many formations, it is necessary for the wellbore completion to control the quantity of sand and other fine particles that enters the production tubing and is brought to surface with the production fluid. A wide range of sand control technologies are used in the industry, and typically comprise a system of sand control devices (such as sand screens) displaced along the completion string which filter sands and fine particles from the reservoir fluids and prevent them from entering the production tubing.
Sand control devices are typically used in conjunction with one or more gravel packs, which comprise gravel or other particulate matter placed around the sand control device to improve filtration and to provide additional support to the formation. In a gravel pack operation, a slurry of gravel solids in a carrier fluid is pumped from surface along the annulus between the sand control device and the open or cased hole, and a successful gravel pack requires a good distribution of gravel in the annulus at the sand control device.
In many subterranean formations, a well will pass through be multiple hydrocarbon bearing zones which are of interest to the operator, and it is necessary to gravel pack the individual zones. An example of a multi-zone completion system is shown in FIG. 1. The system, generally shown at 100, includes a production facility at surface, which in this case is a floating production storage and offloading (FPSO) vessel 102, coupled to a well 104 via subsea tree 106. The wellbore in this case is an inclined wellbore which extends through multiple production intervals 107a, 107b, 107c in the formation 108. The production tubing 110 provides a continuous flow path which penetrates through the multiple zones. The production tubing is provided with ports or inflow control devices (not shown) which allow production fluid to flow into the production tubing and out to the subsea tree 106. In order to provide control over the production process, the annulus 112 is sealed by packers 114 between the different production zones 107 to prevent fluid flowing in the annulus between the different zones. Sand control devices 116 prevent solid particles from the gravel pack and the formation entering the production tubing.
In a conventional approach to sand control, a gravel pack is installed across the first isolated zone 107c by running gravel pack tools in a dedicated gravel pack operation. Subsequently, in a separate gravel pack operation, a gravel pack is installed across an adjacent isolated zone 107b. The procedure can be performed multiple times to place gravel packs across all zones of interest. In some formations, where adjacent zones are particularly close together, it may not be possible to perform separate gravel pack operations. Even where it is possible to perform separate gravel pack operations, it is desirable to install gravel packs across all zones of interest in a single trip when multiple production zones are in close proximity to one another. Such tool systems and methods are referred to as single trip multi-zone systems. In these methods, the gravel pack slurry is pumped with the gravel pack tools positioned across each of the intended zones and the gravel is placed across multiple zones in a single trip, but with distinct and separate pumping operations for each zone. These single trip multi-zone systems reduce the overall time of the gravel pack operation significantly but do suffer from some major disadvantages. For example, the operations are complicated and require a lot of specialized equipment to be installed into the wells; service tools must be repositioned for gravel packing each zone; and pumping must be stopped upon the completion of one zone, and restarted when the tools have been positioned at the next.
To improve the delivery of gravel slurries, sand control devices have been provided with shunt tubes, which create alternate flow paths for the gravel and its carrier fluid. These alternate flow paths significantly improve the distribution of gravel in the production interval, for example by allowing the carrier fluid and gravel to be delivered through sand bridges that may be formed in the annulus before the gravel pack has been completed. Examples of shunt tube arrangements can be found in U.S. Pat. No. 4,945,991 and U.S. Pat. No. 5,113,935. The shunt tubes may also be internal to the filter media, as described in U.S. Pat. No. 5,515,915 and U.S. Pat. No. 6,227,303.
U.S. Pat. No. 6,298,916 describes a multi-zone packer system which comprises an arrangement of cup packers with shunt tubes used in a gravel pack operation. An upper packer is bypassed by a crossover device to deliver the gravel pack slurry to a first production zone, and the shunt tubes allow the slurry to be placed at the subsequent zones beneath the zonal isolation packers. U.S. Pat. No. 7,562,709 describes an alternative method in which the zonal isolation is achieved by the use of swellable packers, which include a mantle of swellable elastomeric material formed around a tubular body. Shunt tubes run underneath the swellable mantle to allow the gravel pack slurry to bypass the isolation packers.
It is also proposed in WO 2007/092082 and WO 2007/092083 to provide packers with alternate path mechanisms which may be used to provide zonal isolation between gravel packs in a well, and embodiments described in WO 2007/092082 and WO 2007/092083 include packers with swellable mantles which increase in volume on exposure to a triggering fluid. US 2010/0155064 and US2010/0236779 also disclose the use of swellable isolation devices in shunt tube gravel packing operations.
Although the above-described shunt tube systems allow zonal isolation in gravel pack operations, the reliance on shunt tubes as a bypass mechanism for gravel slurry placement is undesirable. Reliance on shunt tubes adds to the general complexity of the completion and installation operation. For example, shunt tubes must be aligned and made up to jumper tubes of adjacent sand control devices when the production tubing is assembled.
The use of shunt tubes may also cause complications for maintaining the required annular barrier or fluid seal functions of the isolation packers, as they are required to be actuated to expand around shunt tubes. In swellable elastomer systems, problems may arise due to removal of a volume of elastomer from the isolation device, improper sealing around the shunt tubes, displacement of the conduits due to expansion of the element, and/or coupling of the conduits at opposing ends of the isolation device. Accommodation of shunt tubes may necessitate a reduction in the overall volume of the expanding element, and in particular a reduction in the volume of the expanding element which is radially outward of the shunt tube. A shunt tube system with swellable isolation may therefore take longer than desirable to achieve a seal and/or may not have sufficient pressure sealing performance. Mitigating these problems may require the run-in diameter of the swellable packer to be increased, which can impact on the success of deployment operations, or reduction in the effective production bore size, which is detrimental to production rates.
While the use of swellable elastomer packers and isolation devices have several advantages over conventional packers including passive actuation, simplicity of construction, and robustness in long term isolation applications, their use in conventional gravel pack applications described above may increase the time taken to perform the entire gravel pack operation. This is because in a conventional approach, the isolation devices are set against the wall of the open or cased hole to isolate the zones prior to placement of the gravel pack. This sequence means that the gravel pack cannot be placed until the swellable isolation device has swollen, which in many cases may be a number of days. This introduces a delay before pumping of the gravel slurry which may be undesirable to the operator.